VW Polo Defroster System Failure and Repair Guide

Having some experience with similar heating issues, I dealt with this exact problem on my 2014 VW Golf. The symptoms were identical, complete failure of both front and rear defroster systems. After bringing it to the workshop, they diagnosed a heavily discharged battery causing insufficient power for the thermal window systems. The auto defrost functions are quite sensitive to voltage fluctuations. The total repair cost was 290€, which included a new battery and system diagnostics. Here are the specific issues they found: Battery voltage was too low to power defroster elements, System threw error codes due to insufficient power, Both front and rear defroster were affected The fix was straightforward once properly diagnosed. The whole repair took about 2 hours, including testing all defroster functions after battery replacement. Could you share: Current battery age? Do you notice other electrical issues like slow starter motor? Are there any other warning lights on the dashboard? Have you checked the fuses specifically for the defroster circuits? This information would help determine if your issue matches what I experienced or if its something different in your heating system.

Just had the car serviced last month at 19726km and they did a full electrical check, battery was showing good voltage readings throughout. The error codes are definitely defroster specific, not related to general electrical systems. The starter works fine and all other electrical components function normally. Tested all the fuses for the rear defroster and window demister circuits, they are intact. Wondering if this points more toward faulty heating elements or control module issues rather than power supply problems. The auto defrost system suddenly failed without any warning signs before that. Would testing the individual heating elements help narrow down if its a rear defroster grid issue versus a control module problem?

Your situation definitely sounds different from my battery-related experience. Since you have confirmed good voltage and working fuses, I suspect we are looking at either faulty heating elements or a control module issue in your case. On my VW Golf, when I had a follow-up issue months after the battery replacement, it turned out to be corroded connections at the rear window heating terminals. The thermal window system would intermittently fail, showing similar symptoms to what you describe. The workshop tested the rear defroster grid with a multimeter to check for continuity across the heating elements. This is definitely worth doing as it can quickly identify if you have broken heating elements or poor connections. In my case, cleaning and reseating the connections restored proper function to both the front and rear window heating systems. The labor cost for testing and repairing the connections was around 120€. Much better than replacing the entire window demister control module, which can run 400-600€ depending on the specific part needed. Since your auto defrost stopped working suddenly, checking these connections first makes sense before assuming a more expensive control module failure.

Thanks for the detailed feedback. Those costs are much more reasonable than I was expecting, especially if its just corroded connections causing the car defrost issues. I will get the heating elements tested with a multimeter first. Makes sense to check the simpler fixes before jumping to control module replacement. From what you described, the symptoms do sound similar with the sudden failure of the thermal window systems. I can access the rear defroster connections fairly easily to check for corrosion. Will test both the front and rear window heating terminals since both are affected. If cleaning the connections doesnt resolve it, at least I will know to budget for the more expensive control module repair around 500€. Really helpful to hear about your actual repair experience rather than just guessing at what might be wrong with the auto defrost system. Will update once I figure out the root cause of my defroster problems.